In the course of some studies (1) on the
vasomotor activity in human fingers I noted that
definite circulatory changes occur during
spontaneous yawning. An attempt to correlate
these observations with existing data on yawning
revealed that the few pertinent studies of this
subject have not found their way into British or
American pub1cations. Although yawning and its
associated phenomena appear to be of minor
importance they are not without interest, and it
would seem worth while to make readily available
the little that is known and the rather more
that has been postulated on this subject. Such
is the purpose of this paper.

LITERATURE. Standard sources. It is
well to review the popular conceptions of
yawning as set forth in the standard
physiologic, psychologic and lay publications
before turning to the special literature.

Of the well-known text-books of physiology
eight (2, 3, 4, 5, 6, 7, 8, 9) contain no
discussion of yawning. One of them (10), in a
section devoted to "modified respiratory
movements," defines it in the following
terms:

Various psychic or emotional reactions
manifest themselves not only by facial
expressions, but also by objective changes in
respiratory acts .... Yawning is associated with
a prolonged inspiration during which the mouth
is stretched wide open, followed by a short
expiration. (p. 386)

The larger text-book of Schafer (11), in a
discussion of "modified respiratory movements,"
does not go beyond stating:

Yawning consists of a deep inspiration
accompanied by a wide opening of the mouth and
of the glottis, often attended by movements of
the arms. (Vol. II; p.309)

Even the ponderous German hand-books on
physiology treat the subject in cursory fashion.
Thus in Hermann's Handbuch der Physiologie (12),
under the heading "special forms of respiratory
movements," yawning is defined and dismissed in
these terms:

[yawning is} a psychically or reflexly
excited inspiration during which the vocal cords
may be set in motion. (B. IV; H. 2; S. 234)

In Nagel's Handbuch der Physiologie des
Menschen (13) the topic is introduced and
concluded with the following remarks in a
section devoted to "special forms of
respiration":

The yawn is a deep inspiration carried out
with widely opened glottis and usually with
opened mouth; it is frequently accompanied by
movements of the arms, etc. It is caused by
certain psychic influences, fatigue, etc. (B. I;
S. 27)

From the foregoing it is apparent that while
none of these authors makes any conjecture as to
the physiologic significance of the act, they
have all focused their attention upon its
respiratory component and have classified it as
a respiratory phenomenon. It is hardly necessary
to point out that the subject has not been
developed beyond or even through the descriptive
phase.

The psychologic literature appears to be
equally barren. Yawning has been defined (14) as
" ....a reflex usually induced by bodily
fatigue," but critical studies in support of
this conception are wanting. In a recent review
of the psychologie aspects of the subject Moore
(15) points out that nothing about yawning has
been established beyond the notation that it
appears very early in extra-uterine life.

Articles for lay consumption are more
explicit and display less hesitancy in assigning
a significance or purpose to the yawn. This is
evident in the following excerpt from a recent
New York Times Magazine (16):

Boredom, hunger, overeating, drowsiness and
bad ventilation have all been blamed for yawns,
but the specific stimulus that starts the reflex
is still obscure. The power of suggestion has a
lot to do with it. Yawns are catching, as
everyone knows, and they can even be
self-induced ..... yawn has all the beneficial
effects of a deep breath of fresh air. It is
relaxing and refreshing. It tones up the muscles
of the mouth, the chest, the back and even the
arms. Whether it has any other psychological or
physical effects science doesn't say.

The above views are essentially the same as
those which Clarkson (17) submitted to the laity
in Hygeia. They constitute a modern version of
the Delsartean concept (18) which we will review
in a later paragraph.

It is of interest to compare all of the
foregoing descriptions with the dictionary
definitions of the word yawning and its alleged
synonyms, pandiculation, oscitation and chasma.
Standard lay (19, 20) and medical (21)
dictionaries agree that the word yawning is
derived from the Old English verb ganien which
has always denoted an "opening" in the sense of
"to gape." The definitions of yawning given by
the lay dictionaries (19, 20) are in such
complete harmony that only one need be
quoted:

An involuntary act, excited by drowsiness,
etc., and consisting of a deep and long
inspiration usually following several successive
attempts at inspiration, the mouth, fauces,
etc., typically being wide open. (20)

Some medical dictionaries (21) conform to
this restricted definition, but others have
expanded the meaning to include the associated
stretching of the limbs. Thus Dorland (22)
offers the following definition of yawning:

Pandiculation; a deep, involuntary
inspiration with the open mouth, often
accompanied by the act of stretching.

From this it also appears that Dorland
regards pandiculation and yawning as
synonyms.

Both lay (19, 20) and medical (21, 22)
dictionaries agree that pandiculation is derived
from the Latin verb pandiculari, meaning "to
stretch oneself." Of these dictionaries only
Dorland, as already noted, offers this word as a
synonym for yawning. The others are in agreement
on a more narrow definition of which the
following is characteristic:

A stretching and stiffening, esp. of the
trunk and extremities, as when fatigued and
drowsy, or after waking from sleep. (20)

All of these dictionaries (19, 20, 21, 22)
offer the words chasma (from the Latin

noun chasm .... a cleft or an abyss) and
oscitation (from the Latin verb oscitare .... to
open the mouth wide) as synonyms for the noun
yawn.

From the above it is evident that the
authorities, both lay and medical, have been
aware of the complexity of the act under
consideration and have been uncertain just how
much of it to include under the designation
"yawn." On semasiological grounds it would
appear desirable to preserve a distinction
between yawning and pandiculation, and to employ
some such expression as "the yawnstretch act"
when the entire complex is intended.

Special sources. (Occurrence). Depending on
the breadth of definition adopted, the
occurrence of yawning throughout the animal
kingdom is more or less widespread. Cramer (23)
points out that the familiar gaping movements of
fishes, amphibians and reptiles simulate the
oral component of yawning in man, but most
observers (24, 25, 26, 27) decline to read true
yawning into this superficial resemblance.
Whether or not the gaping of these lower forms
is accompanied by the respiratory component of
yawning and a generalized stretching is not
known, and it is best to follow Peiper (27) in
reserving judgment on the occurrence of yawning
in these classes.

The data on birds are little more complete,
although the gaping chicken beating its wings on
tip-toe is an eyeryday spectacle. Here a
generalized stretching is seen in conjunction
with gaping, but the question of an associated
respiratory effort has not been answered by
critical observation. It is the impression of
both Heinroth (25) and Cramer (23) that true
yawning is practiced by birds, but Hauptmann
(26) opposes this view.

It is generally agreed (23, 24, 25, 26, 27)
that among terrestrial mammals true yawning and
stretching are to be observed in primates and
carnivores. The situation with regard to
herbivora is not so clear, although most authors
concede that these animals practice stretching.
The failure of the herbivora to exhibit the
gaping component of the yawn-stretch act
constitutes an objection standing in the way of
admitting them into the category of yawners, but
Dumpert (24) has pointed out that since
herbivora are exclusively nose-breathers, even
under conditions of stress, it is unnecessary
for them to add the oral component to the
yawn-stretch act in order to effect ifs
inspiratory phase.

Before leaving the subject of yawning in
animals it is important to mention the possible
relationship of its gaping component to the
"automatic expressions" described by Darwin
(28). The gaping movements of fishes, amphibians
and reptiles may belong to this group of
emotional expressions, and it appears certain
that some of the anthropoids employ the
mouth-act in question for emotional
attitudinization. Finally, as we shall see,
there are those who regard the complete
yawn-stretch complex as but another example of
the automatic expressions like laughing and
crying.

In the case of man little can be added to
the previously noted lay observations on
occurrence. The idea that yawns are "catching"
can be traced back to Mayer (29) who believes
that in some individuals the threshold for this
so-called psychically released yawning is
exceptionally low, and that in such persons
autosuggestion may constitute an effective
stimulus. Cramer (23) and Schrijver (30) hold
that yawning may normally be a symptom of
hunger. They report that it is so regarded by
some of the Continental laity, and Luciani (31)
has been cited as supporting this view. It
should be noted, however, that yawning was not
among the symptoms of the fasting men observed
by Carlson (32).

It has been remarked (24, 33) that among
infants and children, as among many animals,
yawning is more regularly attended by stretching
than is the case among adults. Dumpert (24)
looks upon the adult's yawn, without
pandiculation, as a fractionation of a primitive
yawn-stretch reaction, and he postulates that
such a dissociation is the outcome of acquired
voluntary inhibitions cultivated in accordance
with the demands of "good company." As we shall
see in a subsequent paragraph, this concept
enjoys some support from the fact that man's
ability to yawn without stretching can be lost
in certain disorders of the central nervous
system. There are other observations, however,
which suggest that yawning and stretching are
independent albeit frequently associated acts,
rather than fundamentally conjoined responses.
In the first place, infants under 1 year
frequently yawn without stretching and it is
hardly permissible to regard this as a
fractionation of some basic physiologic pattern
by voluntary inhibitions. Secondly, regardless
of man's age he displays a tendency to yawn
(without stretching) just prior to surrendering
to sleep, and to stretch (without yawning) upon
waking. This too intimates that factors other
than voluntary inhibitions are active in
determining whether pandiculjpn and yawning
occur together or separately.

Yawning under circumstances other than those
already mentioned is probably always
morbid.

Special sources. (Clinical.) Addressing
clinicians in 1908 Geigel (34) lamented the fact
that his teachers had never mentioned yawning
and complained that nowhere could he discover
observations elucidating its physiologic or
pathologic significance. Similar conditions
obtain today although morbid yawning is more
common than our neglect of it would imply.

Geigel's contribution to the subject was
quite limited. He emphasized the value of
yawning as a favorable prognostic sign in
certain acute illnesses and noted its occurrence
in hysterics. Several observers (24, 27, 35, 36)
have remarked the frequency of yawning after
severe hemorrhage. Peiper (27) seeks to explain
this on the basis of his theory (vide infra) of
lowered excitability of the central nersous
system, whereas Nash (36) attributes it to
anoxia and/or arterial hypotension. There are no
experimental data supporting either
explanation.

Cramer (23) and Schrijver (30) have reported
the frequency of excessive yawning in diseases
of the gastro-intestinal tract, especially that
of duodenal ulcer, wherein crises of yawning
sometimes parallel exacerbations of symptoms.
The association of deranged stools and flatus
with morbid yawning so impressed Cramer that he
postulated an auto-intoxication by bacterial
toxins arising from within the bowel as the
causative agent. He reviews the rather meagre
evidence supporting this view.

Neurologists have met with abnormal yawning
rather more frequently than others. Oppenheim
(37), Geigel (34) and Lewy (35) have encountered
it in hysteria, and its occurrence as an aura in
epilepsy has been remarked by Oppenheim 37),
Lewy (35), Wilson (38) and Penfield (39). In
Wilson's experience this aura has been
associated with his so-called "peri-ventricular"
or "visceral" epilepsy wherein the yawn is
followed by voiding of urine, giddiness,
headache and sometimes,vomiting. He suggests
that such cases depend on disorder of visceral
centers in the third ventricle regulating sleep
and fluid interchange, with subsequent spread to
others on the floor of the fourth ventricle.
Penfield (p. 110) gives the clinical details of
such a case.

Among the manifold sequelae of epidemic
encephalitis is that of paroxysmal yawning
usually in conjunction with other, though
varied, neurologie disturbances. Mayer (29),
Wilson (38) and Sicard and Paraf (40) describe
cases from their personal experience, but it has
not been possible to ascribe the symptom to
proven lesions at particular foci in the
neuro-axis. In this connection it is of interest
to record certain impressions which Yakovlev
(41) has formed with regard to derangements of
yawning and pandiculation in other disorders
involving the basal ganglia. In his experience
Huntington's Choreics exhibit a propensity for
yawning and more especially for stretching which
stands in sharp contrast to the behaviour of
Parkinsonics who rarely yawn and never stretch.
Yakovlev emphasizes that these impressions have
been derived from a study of relatively few
cases and stand in need of confirmation by a
test on more material.

Excessive yawning is frequently seen in
patients harboring expanding intracranial
lesions, notably cerebellar abscess or tumor
(35, 36, 37, 38, 42). When attended by abnormal
drowsiness the sign is without localizing value
(37, 38), but its occurrence in an alert patient
suggests to some (38) that a thorough search be
made for third ventricular and hypothalamic
signs. Nash (36) hazards an explanation for the
yawning seen in, the usual run of brain tumor
cases. He states:

The occurrence of yawning, which is
essentially an atypical respiratory act, in
cases of brain tumor can be explained by
irritation of the brain resulting in "afferent"
impulses to the medullary respiratory center,
which modify its rhythmic activity. (p. 92)

Special sources. (Investigative.) Mayer (29)
alone has attempted a systematic investigation
of the yawn-stretch act. By means of the
roentgenscreen, laryngeal mirror and palpation
of muscles he has analyzed the sequence of
events in man when the complete complex,
unmodified by inhibition, is allowed to develop.
For convenience of description he divides the
act into a number of phases:

I. Inspiratory Phase (duration: 4.4 to 6.8
sec.)

A. Initial Part B. Acme (duration: 2.5
sec.)

II. Expiratory Phase

During the initial part of the inspiratory
phase one observes a widening of the chest, a
descent of the diaphragm and larynx, an
elevation of the ali nasi and soft palate, a
downward and backward displacement of the
tongue, an abduction of the vocal cords and an
opening of the mouth. This is occasionally
attended by a subjective crackling in the ears
which is thought (43) to be due to a contraction
of the M. tensor vehi palatini with jerking of
its tendon in the bursa between it and the
pterygoid hamulus.

When the acme of the complex has been
attained one notes that the chest, diaphragm,
larynx, tongue, palate and mouth have maintained
or accentuated their respective movements of the
initial phase. There has, in addition, been a
firm closure of the eyes and a rapid development
of the stretch component. The number and
distribution of muscles recruited for the
stretch are subject to variation and may be
modified by voluntary inhibition. Neck and arm
muscles are most frequently recruited, but those
of the legs, trunk and abdomen may participate.
The probable influence of such widespread
muscular activity upon the venous return, and
secondarily upon cardiac filling, rate and
output, has been recognized (24, 29), but no
studies have been made to confirm this. At the
close of this phase saliva occasionally spurts
from the submaxillary and sublingual ducts,
presumably due to a squeezing of these glands by
the contracting oral musculature.

During the expiratory phase one notes a
short sharp expiration with gradual relaxation
of all previously activated muscles permitting
the return of diaphragm, larynx, tongue, etc. to
their resting positions. Lacrimation and
swallowing may occur at this stage. The former
is believed (44) to be due to an augmentation of
secretion rather than to a simple compression of
the lacrymal glands because the tightest
possible voluntary blepharospasm cannot squeeze
forth tears in an amount sufficient to overflow
thecnjunctival sac. The swallowing is presumed
to depend upon the occurrence of the previously
noted salivation. This final phase of the yawn
is usually accompanied by some such subjective
feeling as relief, satisfaction or
refreshment.

Prior to Mayer's (29) fluoroscopic
observations, which show the diaphragm to
descend and remain relatively fixed in this
position from the initiation until the
expiratory phase of the yawn, Hauptmann (2G) had
arrived at a different opinion as to the
behaviour of this organ. Using a kymographic
method for recording thoracic and abdominal
respiration, Hauptmann was led to believe that
the rhythmic action of this muscle was but
little, if at all, interrupted by yawning. His
view must, of course, give way to that suggested
by the more refined method of fluoroscopy. It is
important to note, however, that Mayer and
Hauptmann agree that yawning effects no ultimate
increase in aeration of the lungs; they argue
that the apneic period following the yawn more
than compensates for any temporary increase in
aeration afforded by a single deep breath.

The neural structures subserving the
complicated yawn-stretch act may conveniently be
thought of as comprising an integrative center
played upon by diverse afferent elements and
discharging over its several efferent channels.
Evidence at hand is insufficient, however, to
establish the location or even the existence of
a "yawn-center" in man or animals. Ellenberger
and Scheunert (45) include yawning among the
functions of the medulla oblongata in dogs, but
they do not submit the evidence supporting this
localization. In man a postulated center has
been variously located in the corpus striatum
(23, 35) and "subcortical ganglia" (24, 27, 29)
on very unsatisfactory evidence. There are,
however, two significant papers bearing on this
question. Gamper (46) has seen the complete
yawn-stretch act in what he describes as a
mid-brain preparation (Arhinencephalie mit
Encephalocele), and Catel and Krauspe (47) have
observed it in a case where only the medulla
oblongata and more caudal portions of the
nervous system were

completely formed (Meroanenzephalie mit
Meroankranie). These observations suggest that
if a yawn-center exists it is to be found in the
medulla oblongata, possibly in the immediate
vicinity of the respiratory and vasomotor
centers.

The so-called psychically released yawning,
or yawning as an apparent consequence of
suggestion, implies that the act can be
initiated by influences emanating from the
highest cerebral levels. Inhibition of the act
by influences arising at these levels is
confirmed by the behaviour of hemiplegic
patients who have lost the ability to
fractionate the yawn-stretch act. Both Dumpert
(24) and Lewy (35) have noted yawning in such
patients attended by stretching movements
confined to the affected (i.e., "paralyzed")
extremities .... doubtless to the amazement of
the patient if not the doctor. Dumpert
emphasizes that although this phenomenon is not
to be seen in all hemiplegies it is consistently
present in given cases.

Activation and possibly inhibitory
modification of yawning by neural elements below
the telencephalon is of course attested to by
the observations of Gamper (46) and of Catel and
Krauspe (47) on their cases of cerebral
malformation. The involuntary nature of most
yawns and their occasional occurrence in
comatose patients (29) likewise argue for
activation from so-called "sub-conscious
levels," but nothing further is known about the
afferent influences exciting this act.

Information regarding the centrally located
efferent pathways subserving the yawn-stretch
act is limited to deductions suggested by the
involuntary activation of paralytic limbs during
yawning. This stretching of limbs deprived of
corticospinal control appears to indicate that
the so-called "extra-pyramidal" pathways play a
significant role in the uninhibited act.

Special sources. (Theories.) Numerous
hypotheses concerning the mechanism and
significance of yawning and stretching have
appeared, and existing data do not suffice to
show which of these are tenable. They are not
mutually exclusive and it is possible that each
contains a grain of truth.

The first theory to find its way into print,
that of the Delsarteans, appeared in Russell's
monograph (18) of 1891. This little book, which
remains the most exhaustive account of yawning
in the English language, defies description and
should be consulted in the original by anyone
interested in whimsical physiology. Suffice it
here to say that yawning is presented as an
"automatic impulse" caused by "bad air in the
lungs," designed by Nature as a "gymnastic," and
intended both to "awaken the respiratory organs
into activity' and to "effect a stimulation of
the brain through increased activity of the
circulation." Although this concept enjoys up
supporting evidence it appears to be the
fore-runner of present day lay belief (16, 17)
and it is not without current favor among
clinicians. Within the past decade Otto (33) and
Seeligmuller (48) have reiterated the notion
that yawning is a gymnastic the practice of
which should be cultivated as a means of toning
up the body or relaxing mental tension.

Hauptmann (26) appears to have been the
first clinician to attempt an interpretation of
the yawn-stretch act. Writing in 1920, he
suggested that this complex is a means of
combating the loss of muscle tone which, along
with tedium, develops as a consequence of
enforced inactivity of the higher cerebral
centers. He emphasized that this augmentation of
muscle tone and metabolism, rather than the deep
inspiratory effort, is the main purpose of the
yawn-stretch act. We have already noted his
contention that any temporary improvement in
aeration due to this inspiratory effort is more
than offset by the period of apnea which follows
the expiratory phase. By this process of
reasoning, but without recourse to precise
measurements, Hauptmann rejects the notion that
yawning bespeaks an anoxia of cerebral tissue.
This conclusion has been widely accepted (24,
27, 29, 35) without confirmatory evidence.

Mayer (29) concluded that the yawn-stretch
act is an automatic expression of cerebral
fatigue in the sense that crying and laughing
are expressions of sorrow and happiness. In this
conclusion he has been joined by several
subsequent writers (10, 27, 35). Mayer goes on
to suggest that the act accomplishes important
but as yet undefined physiologic adjustments in
the state of the circulation and in the
metabolism of the recruited muscles.

Of all hypotheses advanced that of Dumpert
(24) is by far the most elaborate. The salient
features of his concept are as follows:

1. Yawning (the mouth act attended by a deep
inspiration) is but part of the larger
yawn-stretch complex which occurs in many
animals, in infants and in children. This larger
reaction is first regularly dissociated into its
respiratory and stretching components in adult
man, and even here the ability to fractionate
the act can disappear following certain lesions
of the central nervous system.

2. The yawn-stretch act is believed to occur
whenever the cerebral circulation is not
favorably adjusted for maintenance of the waking
and alert states.

3. The yawn-stretch complex or even yawning
alone is thought to effect an augmentation of
the venous return to the heart by means of:

a. The "milking action" of the striated
muscles upon the veins of the limbs;

b. The compressing action of the contracting
abdominal muscles and the descending diaphragm
upon the veins of the splanchnic bed; and,

e. The aspirating effect of the lowered
intra-thoracic pressure upon blood entering the
renae cai'ae during the inspiratory phase of the
act.

4. This presumed increase in venous return
is thought to effect an increase in the rates of
cardiac filling and output (Bainbridge's
reflex), thereby providing a generalized
improvement in the supply of arterial blood to
the tissues.

5. A differential distribution of the
supposedly augmented arterial flow is presumed
to occur for the especial benefit of the
cerebral circulation. This selective
redistribution is believed traceable to the
effects of centripetal impulses arising in the
stretched muscles and serving to:

b. Effect a cerebral vasodilatation by their
action on Weber's center.

6. Thus the yawn-stretch reaction and, less
effectively, the yawn alone are able to combat
cerebral circulatory states unfavorable to the
maintenance of the waking and alert
conditions.

Although much that Dumpert postulates is
probable and my own observations (vide infra)
confirm the occurrence of the systemic
vasoconstriction he predicted, his theory is
without support at its crucial points. Thus it
is unjustifiable to assume that the cerebral
circulation is diminished during sleep; indeed,
the only reliable information (49) we have on
the state of the cerebral circulation prior to,
during and after sleep fails to disclose any
significant variations. Further, there are no
observations confirming an increase of the
venous return during yawning. Finally, Dumpert
invokes the aid of a cerebro-dilatory center the
existence of which is open to question.

Peiper (27) looks upon yawning as a purely
respiratory act which represents a transient
disorder of the respiratory center. He believes
that as a result of fatigue the excitability or
sensitivity (erregbarkeit) of the higher
respiratory centers (50) is depressed whereupon
a lower lying yawn-center is released. He thus
explains the occurrence of an automatic
expression of fatigue and does not postulate
that it accomplishes any physiologic
adjustments. His theory is attractive but rests
upon purely hypothetical considerations.

One further theory concerning the yawn has
come to my attention. It has been suggested that
as the nuchal muscles are recruited in the
stretch they squeeze upon the thyroid gland,
express thyroxine into the blood stream and
thereby accelerate the metabolism. The
literature has been searched in vain for the
origin and subsequent reference to this
idea.

NEW OBSERVATIONS. Methods and
material. My observations on yawning were made
while studying the vasomotor activity in the
digits of adult humans some of whom were
"normal" and others of whom were victims of
either Raynaud's or (early) Buerger's diseases.
The diseased group was studied both before and
after therapeutic pre-ganglionic sympathectomy.
None was aware of my interest in yawning.

The subject, comfortably seated, placed one
finger or toe, without restraining device, on a
simple rest between a photo-electric cell and a
constant light source. Current set up in the
cell by light passing through the digit was led
to a 2-stage amplifier, whence it emerged to
activate a DuBois oscillograph. A mirror mounted
on the latter directed a beam of reflected light
onto a moving strip of bromide paper. The
electrical circuit employed was such that a
downward deflection on the photographic record
was produced by an increase in the amount of
light (and decrease in the amount of blood)
traversing the digit.

A stethograph of the air-transmission type
was applied to the chest and its indicator made
to cast a second shadow on the sensitized paper.
A downward excursion of this indicator was
produced by an inspiratory movement.

Tracings of a time-marker and a signal
magnet also appear on the photographic
records.

Subjects were routinely observed over
periods of 30 to 60 minutes in a warm darkened
room. Under these conditions spontaneous yawning
was frequent.

Observations. In the digits of normal adults
a vasoconstriction was regularly observed to
follow a spontaneous yawn. Figure 1 is a
characteristic record of the development and
subsidence of this phenomenon in a finger. From
this tracing if-can be seen that the
vasoconstriction begins to appear after a
latency of about 4 to 4.5 seconds as measured
from the inception of the inspiratory phase of
the yawn. The response is maximal within 9 to 10
seconds after the onset of the yawn and then
gradually subsides during the ensuing 45
seconds. In a large number of such observation
the latent period was regularly found to be
between 3.5 and 5 seconds. The magnitude of the
response and the time required for its complete
development and subsidence were subject to
considerable variation even in the same
individual. In general these values were roughly
proportional to the depth and duration of
inspiratory movement. Maximal response was
nearly always evident within 7 to 12 seconds and
subsidence was usually complete within 30 to 60
seconds.

It was also observed that yawning in normal
adults is regularly attended by a transient
cardiac acceleration. This speeding of the heart
was found to develop and subside pari passu with
the vasoconstrictor response. The subject in
figure 1, whose resting pulse is 80/mm., shows
an acceleration to 90/mm. This degree of cardiac
acceleration, is fairly representative of many
similar observations lut it is subject to
variation among different inthviduals and even
in the same individual according to the depth of
the yawn.

That the observed changes in the
translucency of digits during a yawn are truly
vasoconstrictor responses dependent upon the
integrity of the autonomic innervation of the
part is clearly shown by studies on
sympathectomized extremities. Prior to surgical
intervention the digits of such limbs exhibited
responses equal to or even greater than those
observed in normal parts. Following
sympathectomy they show a greatly diminished or
no vasomotor response depending upon the
completeness of the denervation. Figure 2, a
tracing from the finger of a Raynaud patient
after sympathectomy, shows no appreciable
vasoconstriction following a deep yawn. It is
interesting to note, however, that the cardiac
acceleration is not abolished. This subject's
resting pulse rate of 70/mm. is raised to one of
80 to 85/mm. during the inspiratory phase of the
yawn.

Results in every way comparable to those
depicted for fingers were obtained from the toes
of normal and sympathectomized subjects.

DISCUSSION. Although Dumpert (24) and
Mayer (29) predicted that circulatory
alterations would be found to accompany yawning,
there has been, to my knowledge, no previous
demonstration of such changes. The phenomena
under consideration are, however, closely
related to or identical with the circulatory
changes which Bolton et al. (51) describe as
following a deep inspiration.

In a series of experiments on man Bolton et
al. showed that following a deep voluntary
inspiration a vasoconstriction occurs in the
digital vessels. Its reflex nature was
conclusively established by experiments on
denervated and sympathectomized limbs, and some
evidence was adduced in favor of the afferent
stimulus arising from the expansion of the chest
wall. Figure 3 is a recording by our apparatus
of the vasomotor reflex they describe.

In the discussion of their observations
Bolton et al. make no mention of their reflex
being accompanied by a cardiac acceleration.
Careful scrutiny of their figures 2 and 3
suggests, however, that this did occur in their
experiments. The subject of my figure 3
exhibited a resting pulse rate of 70/mm. This
rose to 80/mm. during the 10 seconds following
the initiation of the deep inspiration and is
typical of the behaviour of the pulse in many
such observations.

SUMMARY The literature on yawning and
stretching has been reviewed. The descriptive
phase of the subject is essentially complete for
man. The experimental phase is barely begun with
the demonstration that irclatory changes
consisting of transient cardiac acceleration and
digital vasoconstriction attend spontaneous
yawning in man. Aspects of the problem remaining
completely unexplored include:

a. The behaviour of the cerebral
circulation;

b. Measurements of cardiac filling and
output;

c. The chemistry of the respiratory
component;

d. The nature of the motor discharge in the
stretch component; and,

e. The possibility of endocrine (e.g.,
thyroid) changes.

Until such observations are completed, any
formulation of the physiological significance of
this act will rest upon an insecure
foundation.

Töpper
R, Mull M, Nacimento W Involuntary
stretching during yawning in patients with
pyramidal tract lesions: further evidence for
the existence of an independent emotional motor
system European J Neurology 2003;10:495-499